Manufacture of lamps of the compact arc discharge type

ABSTRACT

A method of assembling and processing a lamp, particularly the compact arc discharge type of lamp which operates at high temperature and employs regenerative cycling to prevent evaporation of electrode material onto the bulb wall. A quartz envelope is provided, having first and second elongated tubular stems extending from a bulb portion. A pair of elongated electrode assemblies are positioned in the stems, with the ends thereof extending into the bulb portion. An inert gas is flowed into the first stem and hence through the envelope, while the second stem is being heated. The second stem is pinch-sealed to its electrode near the outer end thereof, and then a vacuum is applied at the first stem so as to draw the heated inner portion of the second stem tightly against its electrode. Metal iodide or other desired material is dispensed into the envelope through the first stem, and argon or other desired fill gas is let into the envelope through the first stem, at a pressure less than atmospheric. The second stem then is heated and pinch-sealed to its electrode near the outer end thereof, whereupon the less than atmospheric pressure in the envelope draws the heated inner portion of the first stem tightly against its electrode.

Primary Examiner-John F. Campbell Assistant Examiner-Richard Bernard Lazarus Attorney-Norman C. Fulmer, Henry P. Truesdell, Frank L. Neuhauser, Oscar B. Waddell and Joseph B. Forman United States Patent 1151 3,685,880 Sobieski [45] Aug. 22, 1972 1541 MANUFACTURE OF LAMPS OF THE 57 COMPACT ARC DISCHARGE TYPE A method of assembling and processing a lamp, par- [72] Inventor: John C. Sobieski, Russell Township, ticularly the compact arc discharge type of lamp Ohio which operates at high temperature and employs regenerative cycling to prevent evaporation of elec- [73] Asslgnee' General Elecmc Company trode material onto the bulb wall. A quartzenvelope is [22] Filed: July 6,1970 provided, having first and second elongated tubular stems extending from a bulb portion. A pair of elon- [211 Appl' 52392 gated electrode assemblies are positioned in the stems, with the ends thereof extending into the bulb portion. [52] U.S. Cl ..3l6/19 An inert g is o e into he fir stem and ence 51 1m. (:1 .1101] 9/18 through the envelope, while the second Stem is being [58] Field of Search ..3l6/l8, 19, 20, 1, 17 heated- The Second Stem is Pinch-Sealed to its electrode near the outer end thereof, and then a vacuum is 5 References Cited applied at the first stem so as to draw the heated inner portion of the second stem tightly against its elec- UNITED STATES PATENTS trode. Metal iodide or other desired material is dispensed into the envelope through the first stem, E2222? and argon or other desired fill gas is let into the en- 276l087 8/1956 Bowteli 6/20 X velope through the first stem, at a pressure less than 3l94625 7/1965 D k 316/20 atmospheric. The second stem then is heated and lsll 10/1965 j "316/19 pinch-sealed to its electrode near the outer end 3462209 8/1969 33 r "316/19 thereof, whereupon the less than atmospheric pressure in the envelope draws the heated inner portion of the first stem tightly against its electrode.

3 Claims, 6 Drawing Figures PMENTED 3.885.880

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1TWVTTTOTI John C. Sobieski His A t lrorneg MANUFACTURE OF LAMPS OF THE COMPACT ARC DISCHARGE TYPE BACKGROUND OF THE INVENTION The invention is in the field of lamp manufacture, and is particularly applicable to the combined assembly and processing of compact arc discharge lamps of the type which operate at high temperature and which employ regenerative cycling to prevent evaporation of electrode material onto the bulb wall.

Many methods have been devised for making lamps. A much-used two-step process consists of first assembling the lamp, and then evacuating the lamp and/or providing a fill of inert gas (and/or metallic compounds) through a tubulation extending from the bulb or stem of the lamp. The tubulation is then sealed off. In assembling the lamp, one or more of the leads may first be sealed through a glass stem, and the stem is then sealed to the bulb by means of heating and forming with jaws or by pulling a vacuum to draw together the heated regions of the stern and bulb. Instead of employing a stem, the leads can be beaded with a glass globule, or sealed through a metal disc or cap, whereupon the bulb is sealed to the glass bead, or metal disc or cap, by heating and forming with jaws and/or vacuum. In another method, the leads are pinch-sealed directly to the bulb.

In the manufacture of compact arc discharge lamps, some of the prior manufacturing methods are not feasible. It is undesirable to provide an exhaust tubulation on the bulb, because the sealed-off tubulation protru sion will degrade the optical qualities of the compact lamp. On the other hand, it is not feasible to provide an exhaust tubulation at a lead-seal region of the lamp, because of the small size. Furthermore, it is undesirable for such a lamp to have an exhaust tip or any other space away from the bulb into which the hot operating metallic compounds can condense and thus change the operating pressure and composition. To further complicate the design and manufacture of such a lamp, because of the hot operating temperature of the bulb, it is desirable to locate the lead seals in elongated stems a distance away from the hot bulb to reduce the likelihood of cracking.

The history of manufacturing compact high-temperature arc lamps is illustrated by U.S. Pat. Nos. 3,067,357 and 3,305,289 to Elmer G. Fridrich, both assigned to the same assignee as the present invention. The earlier of the Fridrich patents illustrates a lamp structure employing an exhaust and processing tubulation extending from the side of the bulb. The later patent discloses a method of simultaneously assembling and processing such a lamp, without any exhaust tubulation, comprising the steps of sealing each elongated electrode into an elongated quartz sealing tube, respectively sealing the sealing tubes to the outer ends of necks extending from a quartz bulb, filling the bulb with inert gas and one or more vaporizable metallic compounds, sealing off the sealing tubes, heating and collapsing the bulb necks over the sealing tubes, and severing the sealing tubes to expose the outer ends of the leads. This process, though it achieves the objective of manufacturing a compact lamp without any tubulation, is expensive inasmuch as it requires six heat-sealing operations in a dual-chuck rotating lathe.

SUMMARY OF THE INVENTION Objects of the invention are to provide an improved method of manufacturing lamps, and to provide an improved and inexpensive method for assembling and processing tabulation-free compact arc discharge lamps of the type which operate at high temperature and which employ regenerative cycling to prevent evaporation of electrode material onto the bulb wall.

The method of the invention comprises, briefly and in a preferred embodiment, the steps of providing an envelope (preferably of quartz) having first and second elongated tubular stems extending from a bulb portion, positioning first and second elongated electrode-andlead assemblies respectively into said first and second stems with the ends of the electrodes extending into said bulb portion and in mutually spaced apart relationship, flowing an inert gas into the first stern and hence through the envelope and out the second stem and simultaneously heating the second stem, pinch-sealing the second stem to the lead of the second electrodeand-lead assembly, applying vacuum at the first stem to draw the heated inner portion of the second stem against the second electrode, introducing fill matter into the envelope through the first stem at a pressure less than atmospheric, heating the first stem, and pinchsealing the first stem to the lead of the first electrodeand-lead assembly, whereupon the less-than-atmosphen'c pressure in the envelope draws the heated inner portion of the first stem against the first electrode. In the manufacture of an arc lamp for direct-current operation, the anode electrode is longer than the cathode electrode and preferably is the first electrode to be sealed in the method of the invention.

BRIEF DESCRIPTION OF THE DRAWING FIGS. 1-5 illustrate steps of the method for making a lamp in accordance with a preferred embodiment of the invention; and

FIG. 6 is a side view of a completed lamp made in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. 1, an envelope 11 is provided, preferably of quartz or other suitable vitreous material, having first and second elongated tubular stems 12 and 13 extending from a bulb portion 14. The stems 12 and 13 and bulb 14 are of circular cross section and are aligned along a common axis.

A support and processing chamber 16 is provided with an opening 17 into which the end portion of the stem 12 fits snugly, and is also provided with an electrode assembly holder 18 which holds the lead end 19 of an electrode assembly consisting of an elongated electrode 21 and an elongated lead 22 in spaced-apart axial alignment, and a metal foil 23 welded or otherwise attached to the adjacent ends of the electrode 21 and lead 22. Preferably the electrode 21 is tungsten, and the lead 22 and foil 23 are molybdenum. The foil 23 may comprise a flattened end of the lead 22. The free end of the electrode 21 extends to a desired location within the bulb portion 14 of the envelope 11.

A dispenser 26 is provided on the chamber 16, for dispensing desired metallic compounds into the envelope 14. A simplified way of accomplishing this is to place a pellet of metal iodide or other desired material into the dispenser 26, and rotate a valve 27 when it is desired to dispense the pellet into the envelope l4. Argon or other inert gas is applied to a gas inlet port 31, and a vacuum is applied at a vacuum port 32, these ports being selectively coupled to the chamber 16 by means of a two-way rotary valve 33.

A support jig 36 aids in positioning the lower stem 13, and holds the end 19' of an electrode assembly consisting of an elongated electrode 21 and a lead 22 in spaced-apart axial alignment, with a metal foil 23 welded or otherwise attached to the mutually adjacent ends thereof. An opening 37-is provided in the jig 36, for the escape of argon gas when argon is flowed through the envelope 1]. The free end of the anode electrode 21 extends into the bulb portion 14 of the envelope 11, in suitably spaced relationship to the end of the cathode electrode 21. In the construction shown, the lamp is intended for direct current operation, the upper electrode 21 being the cathode and being relatively slender and having a tapered point, and the lower electrode 21' being the anode and being relatively longer and larger in diameter than the cathode electrode 21, because the anode operates at a considerably higher temperature than does the cathode electrode.

As shown in FIG. 1, one or more burners 41, 42 are positioned to heat the entire quartz stem 13 to a plastic condition. At the same time, the valve 33 is turned to the position shown, so that argon or other inert gas flows through the envelope 11 to prevent oxidation of the electrode assembly 1 In FIGS. 2-5, the electrode assemblies 20 and 20' are shown as being rotated 90 with respect to their positions in FIG. 1, in order to more clearly illustrate the steps of the invention. As shown in FIG. 2, a pair of jaws 46 and 47 press against opposite sides of the stem 13 and seal it to the metal foil 23'. This is called a pinch seal". Immediately upon making the pinch seal at stem 13, the valve 33 is turned to open the vacuum port 32 to the envelope 11, and the vacuum draws the hot remaining portion of the stem 13 tightly against the electrode 21, as indicated by the arrows 48 in FIG. 3. Thus, the stem 13 is fitted snugly against the electrode 21, to prevent any space in the envelope 11 away from the bulb portion 14 which will be relatively cooler than the hot bulb portion 14 when the lamp is operating and into which the hot operating gaseous metallic material of the lamp can condense and undesirably affect the pressure and composition of the lamp fill, and this has been accomplished quickly and inexpensively by the aforesaid step of pulling a vacuum in the envelope immediately after the pinch seal has been made and while the stem is still hot and in a plastic condition. This is made possible by the fact that as soon as the pinch seal has been made, it is possible to pull a vacuum in the envelope.

Next, as shown in FIG. 4, the dispenser valve 27 is rotated to dispense a pellet of metal iodide or other desired material into the envelope ll, whereupon the dispenser valve 27 is immediately closed. The valve 33 t is returned to its position for admitting argon gas into the envelope 11, the argon being at a desired pressure which is less than atmospheric when the lamp is cool and is much greater than atmospheric pressure when the lamp becomes hot during operation. The cathode stem 12 of the lamp is heated by flame from the burners 41 and 42, and then a pinch seal is made at the metal foil 23 by jaws 46 and 47, as shown in FIG. 5. Since the entire stem 12 has been heated to a plastic condition, the less than atmospheric pressure inside the bulb 14 causes the inner end of the stem 12 to draw tightly against the cathode electrode 21 all the way to the bulb portion 14.

The lamp is completed by cutting or breaking off the end portions of the stems 12 and 13 beyond the pinch seals, and the completed lamp appears as shown in FIG. 6, having been completely assembled and processed by the relatively few simple steps described above, requiring only two sealing operations instead of the six that are required in the above-mentioned prior US. Pat. No. 3,305,289. A typical size for such a lamp, is approximately 1 to 2 inches long (exclusive of leads) and about one-fourth to one-half of an inch maximum outside bulb diameter.

For an arc lamp intended for alternating current.

operation, the two electrodes are identical and the same length, and therefore either of the electrodes may be sealed first. However, in the case of a direct current lamp as illustrated in the drawing, in which the anode electrode 21 is longer than the cathode electrode 21, it is preferred to seal the anode electrode-first because the step of pulling a vacuum in the envelope as shown in FIG. 3 is better capable of drawing the relatively longer stem portion against the electrode 21', than is the less than atmospheric pressure gas fill in the envelope which draws a portion of' the stem against the cathode electrode as shown in FIG. 5.

Although the steps of the invention have been described in a preferred sequence, no specific sequence is necessary forcertain of the steps. However, two steps that must be performed in proper sequence are the making of the first pinch seal and then pulling a vacuum to draw the stem against the electrode.

While a preferred embodiment of the invention has been shown and described, other embodiments and modifications will be apparent to persons skilled in the art, and will fall within the scope of invention as defined in the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is: A

1. A method of assembling and processing an arc discharge lamp, comprising the steps of providing a lamp envelope having first and second elongated tubular stems extending outwardly from a bulb portion, positioning first and second elongated electrode-andlead assemblies respectively into said first and second stems with the ends of said electrodes extending into said bulb portion in mutually spaced apart relationship, flowing an inert gas into said first stem and hence through the envelope and out said second stem and simultaneously heating substantially the entire length of said second stem, sealing a portion of said second stem to the lead of said second electrode-and-lead assembly at a region spaced from said bulb portion, applying a vacuum through said first stern while said second stem is hot thereby drawing said second stem inwardly against said second electrode in the region between said seal and said bulb portion, introducing fill material and gas into the envelope through said first stem at a pressure less than atmospheric, heating the first stem over substantially the entire length thereof, and sealing a portion of the first stem to the lead of said first electrode-and-lead assembly at a region spaced from said bulb portion, whereupon said less-than-atmospheric pressure in the envelope causes the first stem to be drawn inwardly against said first electrode in the region between said first stem seal and said bulb portion.

2. A method as claimed in claim 1, in which said lamp is intended for direct current operation whereby the anode electrode is longer than the cathode electrode, comprising the additional steps of using the electrode-and-lead assembly of the relatively shorter of the electrode-and-lead assembly that is positioned in the stem. 

1. A method of assembling and processing an arc discharge lamp, comprising the steps of providing a lamp envelope having first and second elongated tubular stems extending outwardly from a bulb portion, positioning first and second elongated electrodeand-lead assemblies respectively into said first and second stems with the ends of said electrodes extending into said bulb portion in mutually spaced apart relationship, flowing an inert gas into said first stem and hence through the envelope and out said second stem and simultaneously heating substantially the entire length of said second stem, sealing a portion of said second stem to the lead of said second electrode-and-lead assembly at a region spaced from said bulb portion, applying a vacuum through said first stem while said second stem is hot thereby drawing said second stem inwardly against said second electrode in the region between said seal and said bulb portion, introducing fill material and gas into the envelope through said first stem at a pressure less than atmospheric, heating the first stem over substantially the entire length thereof, and sealing a portion of the first stem to the lead of said first electrode-and-lead assembly at a region spaced from said bulb portion, whereupon said less-than-atmospheric pressure in the envelope causes the first stem to be drawn inwardly against said first electrode in the region between said first stem seal and said bulb portion.
 2. A method as claimed in claim 1, in which said lamp is intended for direct current operation whereby the anode electrode is longer than the cathode electrode, comprising the additional steps of using the electrode-and-lead assembly of the relatively shorter cathode electrode as said first electrode-and-lead assembly, and using the electrode-and-lead assembly of the relatively longeR anode electrode as said second electrode-and-lead assembly.
 3. A method as claimed in claim 1, wherein each of said electrode-and-lead assemblies includes a thin metallic foil section interconnected between ends of the electrode and the lead, and wherein each of said steps of sealing a stem to a lead comprises the step of pinch-sealing a portion of the stem to the metallic foil of the electrode-and-lead assembly that is positioned in the stem. 